1. Field of the Invention
This invention relates to equipment used in the drilling and completion of subterranean wells, and more specifically to equipment used in circulating fluid and in the annular placement of cement between a pipe string and an earthen borehole.
2. Background of the Related Art
Oil and gas is recoverable from geologic reservoirs by drilling a deep borehole into the earth's crust to a petroleum reservoir. Casing is a protective liner comprising many casing segments threadably coupled at the ends to form an elongated string of pipe. The casing string is made up to the desired length and cemented into the borehole by pumping a predetermined volume of cement slurry down through the bore of the casing string and into the casing—borehole annulus along a targeted interval of the borehole. The cement liner formed around the casing string reinforces the casing string, isolates the casing from corrosive elements and prevents unwanted cross-flow between geologic formations penetrated by the borehole.
Proper conditioning of the borehole prior to placement of the cement slurry improves the quality and effectiveness of the cement liner. Sustained circulation of drilling fluid down the bore of the casing string and back to the surface through the annulus suspends and removes unwanted mud filter cake, drill cuttings and other debris that, if left in the annulus, may compromise the quality of the cement liner and lead to well failure. Drillable cement wiper plugs may be used to isolate a pumped volume of cement slurry from the fluid circulated to condition and clean the borehole and to displace cement in the annulus. The drillable cement wiper plugs may be deployed into the bore of the casing string, one ahead of and one behind the cement slurry, to prevent contamination.
Unwanted delays may result from the need for rigging up cement wiper plug launching assemblies or other tools used for cement placement, and from disconnecting fluid lines and connecting cement lines that feed the cement slurry to the bore of the casing string. Prolonged static conditions prior to cement placement may allow cuttings and debris to settle and accumulate at narrow clearances in the annulus. Too often, the delay between circulating fluid to clean the annulus and placement of cement compromises the quality of the cement liner, and there is a need for minimizing or eliminating the delay in order to improve the quality of the cement liner.
Accordingly, there is a need to for a casing make up, running and circulation tool that allows transition from circulation of drilling fluid into the borehole to placement of cement without prolonged delay. There is a need for a casing make up and running tool that allows deployment of cement wiper plugs into the bore of the casing string to isolate the cement slurry from other fluids without prolonged delays for rigging up tools after landing the casing string into the wellbore and circulating the well. There is a need for a casing make-up and running tool that can rotate and reciprocate the casing string during cement placement to improve the cement liner by assuring that cement fills substantially all voids. There is a need for a casing make-up running tool that can selectively be used for fill up of the casing string or circulation of fluid to condition the borehole during casing running operations and for a tool that can transition from conditioning the borehole to the cement placement phase without removing the tool from the casing string. There is a need for a casing make-up and running tool that enables an operator to minimize the amount of time required to convert from casing running configuration to a cementation configuration.